perf: PeriodCombiner improvements (#6005)

Summary of changes:
- create dummy streams during preparing arrays of input streams
- use hash map to quickly find perfect stream matches across periods
- hash map also automatically removes duplicates, so remove previous
logic for finding them
- check earlier are we trying to create output stream from dummy stream
- 2 changes from above also gives us a possibility to simplify
`areCompatible()` & `isBetterMatch()` methods
- reduce creation of spare collections when concatenating streams
- reduce conditional logic when possible

I was testing `PeriodCombiner.combinePeriods()` performance of mentioned
changes on Tizen 2021 on 2 streams and I've got following results:

| content | upstream | proposed changes |
| - | -: | -: |
| stream 1 | 23 ms | 17 ms |
| stream 2 | 484 ms | 191 ms |

Both streams are VOD.
Stream 1 has 18 periods with 6 video & audio tracks in each.
Stream 2 has 18 periods with 6 video tracks & 36 audio tracks in each.

lib/dash/dash_parser.js

@@ -1610,7 +1610,6 @@ shaka.dash.DashParser = class {
         hdr,
         videoLayout: undefined,
         tilesLayout,
-        matchedStreams: [],
         accessibilityPurpose,
         external: false,
         fastSwitching: false,